1. Field of the Invention
The present invention relates to digital image recording and/or reproducing apparatus, and more particularly to such apparatus which are capable of changing a time (or a compression rate) for (or at) which a digital signal is recorded on the same recording medium.
2. Related Background Art
In a conventional apparatus for recording a wideband video signal, a method of changing a track pitch to thereby change the time for which the video signal is recorded on the same recording medium is used as in a well-known video tape recorder (VTR). This method is intended to perform long-time recording by sacrificing the dynamic range of the S/N ratio of a signal to be recorded. In a VTR of this type, it is not difficult to set the track pitch at any value and it is relatively easy to set a desired recording time. Therefore, it is also easy technically to set various recording times.
With the advancement of the recent digital image signal processing techniques, a digital image recording apparatus (DVR) which digitizes a wideband analog signal such as a video signal, digitally modulates the resulting digital signal, records and reproduces the modulated signal has been also developed. In such a DVR, the S/N ratio of the reproduced signal does not depend on the quality of the reproduced data, but reproduction itself would become impossible if the S/N ratio of the reproduced signal decreases below a certain value. Therefore, in such a DVR, to change the track pitch and hence the recording time is senseless because images of the same quality are recorded and reproduced at any track pitch. Thus, it is desirable that in a DVR, a signal is recorded and reproduced with a track pitch determined such that digital data can be recovered sufficiently. It is not conceivable that the track pitch would be further increased or decreased to change the recording time in a DVR of this type.
It has been proposed to enable long-time recording by reducing a quantity of data to be recorded in a DVR of this type. Namely, it has been proposed to change the recording time by changing the number of tracks formed per unit time.
In order to change the quantity of data to be recorded, there are methods of changing the number of bits of each of pixels of a video signal, and methods of changing the sample frequency.
However, in such a DVR, a correct image cannot be obtained even if a quantity of data per unit time may be changed to various values unless reproduction corresponding to those changes in the quantity of data is made. Especially if images are recorded by changing the compression rates of the images picture by picture, it is very troublesome to perform such adjustment.
Conventionally, generally in a DVR, an area where a digital video signal is recorded (a video area) and an area where a digital audio signal is recorded (an audio area) are separately provided on a recording track and those signals are processed, recorded and reproduced by separate corresponding signal processing circuits.
However, in the conventional DVRs, audio data and video data must be processed by separate signal processing systems. In addition, since the audio area is small, all the audio data for one track may be nullified by a long time dropout.